Conventionally, a submarine tank is built on land, in a horizontal position in a dock large enough to hold the entire tank.
A system may be constructed by using as large a tank as possible, for example, a cylindrical tank having a diameter of 100 m and a length of 400 m. Building of such a large tank on land is subjected to various restrictions. Hence, tanks that can be built on land are limited in size.
More specifically, if a large tank is manufactured on the land, its size is limited by the size and proof strength of the dock, and also by the draft of the dock and the depth of the neighboring water passages.
An object of the invention is to provide a method which can manufacture a tank that is too large to be built on land.
Such a large tank finds use in, for example, thermal power plant. A thermal power plant is located near the seacoast in most cases. The carbon dioxide gas (carbon oxide gas) generated in the thermal power plant will result in environmental disruption such as air pollution. Attempts have been made to dissolve the gas in sea water and thereby discard the gas, by using various methods.
More precisely, (1) a method of dissolving the carbon dioxide gas generated in the thermal power plant, directly in sea water; (2) a method of solidifying the carbon dioxide gas into dry ice and sinking the dry ice onto the sea bottom: and (3) a method of liquefying the carbon dioxide gas aboard a ship and dissolving the gas in the sea water, over a sea zone 100 m wide.
With the method (1) it is difficult to dissolve the carbon dioxide gas sufficiently. Furthermore, there exists the danger that the carbon dioxide gas blows up over the sea surface.
The methods (2) and (3) may render the sea water strongly acid. This is because the liquefied or solidified carbon dioxide is dissolved in the sea water, inevitably increasing the carbon dioxide concentration in the sea water, making the sea water strongly acid.
Consequently, the methods (2) and (3) affect the deep-sea life. The methods (2) and (3) may also induce environmental changes because it lowers the temperature of sea water. Further, a great amount of energy is required to perform the methods (2) and (3), in which carbon dioxide is solidified into dry ice and liquefied, respectively.
The present invention has been made in view of the above. An object of the invention is to provide a combined system for deep-sea power storage and carbon dioxide dissolution, which can store power, causing no cavitation of a high-head pump turbine, and which can dissolve and discard carbon dioxide at low cost, not affecting marine ecology or causing environmental changes.
The conventional power system is disadvantageous in the following respect. Hitherto known is a pumped storage power system in which water is pumped up at night by using surplus electric power, and electricity is generated in the day when the power consumption is at its peak. However, geographical conditions for a pumped storage power system are restrictive, and the building cost of the system is increasing much. In view of this, it has become difficult to construct new pumped storage power plants.
Recently a deep-sea power storage system has been proposed as a low-cost power plant. This system has less restriction on its geographical conditions, and can be constructed at low cost. The system comprises a main body and a battery tank. The main body, which has a pump turbine, is installed in the deep sea, together with the battery tank. At night, the surplus power generated on land is used to turn the pump turbine, thereby discharging sea water from the battery tank, and power is stored by virtue of the energy obtained from the water head between the sea level and the sea water level in the battery tank.
In the day when the power consumption is at its peak, sea water is poured into the battery tank, thereby turning the pump turbine and generating electric power, and the power thus generated is supplied to the land.
Jpn. Pat. Appln. KOKAI Publication No. 04-01940 based on a patent application, for example, in which the present applicants are named as inventors, discloses a deep-sea power storage system. In this system, sea water is introduced into the pressure-resistive vessel laid in the deep sea (usually, on the seabed), rotating the water turbine. The water turbine drives the generator, which generates electric power. The power generated is supplied to the land. In the system, the surplus power available on the land is used to drive the water turbine, pumping the sea water from the pressure-resistant vessel, thereby to store the electric power.
Studies must be conducted for the foundation of such a deep-sea power storage system, which is strong enough to withstand earthquakes. This is because earthquakes may happen at the seabed on which the system is installed.
Measures should be established that must be taken to repair the various components of the system, such as the pump turbine, if troubles should develop in these components in the deep sea. Furthermore, measures should be established that must be taken in case cavitation takes place. Cavitation is likely to happen when a vacuum similar to water vapor develops in the space above the sea water level in the battery tank as the pump turbine discharges the sea water from the tank.
The present invention has been made in view of the above. An object of the invention is to provide a deep-sea power storage system which is greatly resistant to vibration, which can easily be repaired, and which can operate reliably.
A conventional submarine power storage system is installed, with the battery tank and electrical/mechanical component cases (containing power-generating equipment, power-storing equipment and the like) provided and secured within the pressure-resistant vessel.
Therefore, an additional pressure-resistant vessel must be used in order to increase the output of the system a little, if necessary to meet an increased demand for electric power. In fact, it would be extremely difficult to satisfy such a demand as described above.
In the case of a pumped storage power plant constructed in a mountainous region, which utilizes the head of a water storage dam, the amount of power it can store is determined by the capacity of the dam. With this plant it is difficult to store more electric power.
In view of this, the present invention has been made. An object of the invention is to provide a submarine power storage system that can have its storage capacity increased even after the commercial operation.
There is the trend of stockpiling LNG, just like petroleum. The annual domestic consumption of LNG is about 55,000,000 m.sup.3 at present. If LNG were to be stored for 120 days of consumption, like petroleum, it should be stored in an amount of 18,000,000 m.sup.3.
In order to store this amount of LNG, 90 LNG tanks are necessary, each cable of storing 200,000 m.sup.3 at most. At present there is no land large enough to build so many tanks. From an economical point of view, too, it is difficult to build these tanks.
It would be dangerous, as is pointed out, that LNG tankers frequently navigate along a gulf coast where thermal power plants are densely constructed, because the LNG tankers may likely to collide with each other.
Hitherto, LNG has been stored in LNG tanks built on the ground or half-buried in the ground. The LNG tanks must be made of press-stressed concrete or high-density reinforced concrete to acquire a press stress and withstand the inner pressure. The use of either material complicates the structure of the LNG tanks. This renders it difficult, from an economical viewpoint, to build LNG tanks of this type.
More precisely, a press stress must be applied to the conventional LNG tanks to prevent a tensile stress from developing even if the inner pressure of the tanks rises. In order to apply a press stress to the tanks, reinforcing bars and tendons are embedded in concrete, extending vertically and horizontally. This inevitably makes the tanks complex in structure.
Moreover, LNG acquires a pressure nearly equal to the atmospheric pressure when it is used. It must therefore be maintained at -162.degree. C. to assume a liquefied state at the atmospheric pressure. This is an absolute requirement that must be fulfilled to attain safety. This maintenance of temperature is a hindrance.
Namely, energy should be used to accomplish forced cooling in order to maintain the gas at -162.degree. C. or less for a long time under the actually applied pressure equal to or less than the atmospheric pressure.
Furthermore, a pump immersed in the LNG contained in an LNG tank is operated, forcing LNG cooled to -162.degree. C. out of the LNG tank and supplying the same. Once a trouble has developed in the pump immersed in LNG, the plant cannot help but be stopped. The pump is, as it were, a lifeline to the plant.
Geographical, economical, cooling and LNG-supplying conditions for an LNG storage system can hardly be satisfied. As a matter of fact, it has hitherto been considered to be difficult to reserve (store) LNG for so long a time as petroleum.
This present invention has been made in view of the above. An object of the invention is to provide a submarine LNG storage system which can be constructed near cities and which can store LNG in great quantities for a long period of time.
Today, tunnels are dug in the seabed, thereby constructing roads and railways, thus providing routes connecting locations on the land.
The technique using a shield machine is employed to build tunnels in the seabed. In the course of building a tunnel in the seabed, large-scale measures must be taken to stop dead water. Besides, it usually takes a long time of period to dig the tunnel in the seabed.
Recently, so-called submerged tunnel technique has come into practical use. This technique is to submerge tunnel units made of concrete in the sea and connect the units in series on the seabed, thereby building a submerged tunnel. With the submerged tunnel technique it is easy to stop dead water. Further, the technique can build a tunnel within a short period of time.
The submerged tunnel technique is carried out as follows. First, concrete tunnel blocks of the type shown in FIG. 45 are made on the ground, each having passages for roads or railways. Then, the tunnel blocks a towed by tugboats to an a building site on the sea, submerged there in the sea, anchored on the seabed and connected in series, thus building a submerged tunnel.
Very recently it has been proposed that big and long tunnel blocks, each having roadbeds and railway tracks, be used to build a submerged tunnel on the seabed. A large-scale transport route can thereby be provided.
It is difficult, however, to manufacture such gigantic tunnel blocks a on the ground, for some reasons. A large land is required, and transport equipment (hoisting system) must be provided. To make matters worse, the manufacturing efficiency is low since the manufacture site extends horizontally and is considerably spacious.
Furthermore, manufacturing tunnel blocks on the ground requires much cost and many man-hours. This is because concrete needs to be deposited in a great amount in order to form the horizontal sections of each tunnel block, and also because many reinforcing members must be laid before concrete is deposited to manufacture each tunnel block.
Also, additional reinforcing members must be used to prevent a tensile stress from developing in the concrete sections while the tunnel block is being made on the ground. More specifically, unless reinforcing bars are laid for preventing a tensile stress, after a block of steel plates has been made, concrete can not be deposited in the steel shell.
This means a reinforcing frame needs to be assembled twice. A considerably high cost and a number of man-hours are required only to deposit concrete.
Due to these facts, it is regarded as impossible to manufacture big and long tunnel blocks a on the ground. Further it is considered difficult to shorten the time of building a submerged tunnel. These hinder the construction of a large-scale submerged tunnel.
In view of this, the present invention has been made. Its object is to provide a technique of building a large-scale submerged tunnel within a short period of time, by using huge concrete tunnel blocks which can be manufactured at low cost.